In an optical module, such as a light emitting module or a light receiving module used for an optical communication device or the like, a light emitting element or a light receiving element such as a laser diode or a photo diode and other components are received in a receptacle. The receptacle can be manufactured at low cost and be handled easily. The light emitting element or the light receiving element and other components are connected to lead terminals by wires or the like for supplying signals or electric power.
In recent large scale optical communication devices, for example, a large number of the optical modules are provided in an optical module mounting part in parallel so that parallel transmission of a large number of optical signals is realized.
FIG. 1 is a schematic cross-sectional view illustrating a structure of a related art optical module.
Referring to FIG. 1, at the time of communication, an external line optical cable 2 is connected to an optical module 1 such as a light emitting module or a light receiving module used for an optical communication device or the like.
The optical module 1 includes a housing 3 made of metal. A receptacle 4 and an optical connector 5 are provided inside the housing 3. An optical semiconductor element (not illustrated) which is a light emitting element or a light receiving element such as a laser diode or a photo diode is provided inside the receptacle 4. The optical connector 5 is provided at a head end part of the external line optical cable 2.
The receptacle 4 having an inside where a ferrule 6 is received includes a first stub part 4a, a brim part 4b, and a second stub part 4c. The first stub part 4a is provided at a head end side of the receptacle 4. The first stub part 4a is provided in a concave part of the optical connector 5 and configured to guide an internal surface of the concave part. The brim part 4b has a diameter greater than that of the first stub part 4a. The second stub part 4c has a diameter greater than that of the first stub part 4a and smaller than that of the brim part 4b. The second stub part 4c is provided at the optical semiconductor element side. The ferrule 6 is provided inside the second stub part 4c and holds the brim part 4b. 
A convex part 7 is provided at a part of the inside the housing 3, the part being where the first stub part 4a, the brim part 4b, and the second stub part 4c of the receptacle 4 are positioned. In addition, a groove part 8 is formed in the convex part 7. The receptacle 4 is provided inside the housing 3 so that the brim part 4b is positioned in the groove part 8.
The optical semiconductor element provided inside the receptacle 4 is connected to a printed wiring board 9 via a flexible wiring board 10. An LSI (Large Scale Integrated Circuit) and others are provided on the printed wiring board 9.
On the other hand, an external surface of the optical connector 5 is guided by an internal wall part of the housing 3. In addition, a ferrule 11 is provided inside the optical connector 5. The ferrule 11 has a cylindrical-shaped configuration so that the external line optical cable 2 is held and fixed.
The ferrules 6 and 11 are arranged precisely by a line sleeve 12 so as to stand in a row. The line sleeve 12 is formed inside the first stub part 4a, the brim part 4b and the second stub part 4c. By connecting the ferrules 6 and 11 to each other, the optical semiconductor element provided in the receptacle 4 and the optical connector 5 are optically and precisely connected to each other.
Under this structure, the ferrules 6 and 11 are connected to each other by fixing the center of the receptacle 4 where the ferrule 6 is received in a center position of the housing 3 and inserting and engaging the optical connector 5 provided at the head end part of the external line optical cable 2 to the housing 3. As a result of this, the optical semiconductor element provided in the receptacle 4 and the optical connector 5 are optically and precisely connected to each other and thereby optical communications are performed.
An optical receptacle having the following structure is described in Japanese Laid-Open Patent Application Publication No. 2006-178384. The optical receptacle has a blind-cup shaped metal holder having an opening part in which a through-hole is formed on the bottom surface; a fiber-stub in which an optical fiber is fixed on the center of a ferrule and the back end part is inserted and fixed into the through-hole of the metal holder; a split sleeve for inserting a tip part of the fiber-stub from one side opening end part, abutting the plug ferrule inserted from the other side opening end part to the top end surface of the fiber-stub and clamping the fiber-stub; and a tubular case. A pin abutted to the outer peripheral surface of the split sleeve, which is extended by inserting the plug ferrule into the split sleeve, is attached to the inner peripheral surface of the case.
An optical fiber connector is described in Japanese Laid-Open Patent Application Publication No. 2002-250840. A reinforcing sleeve is arranged on the outside of a split sleeve for aligning an optical fiber, with a float-structure clearance provided for a sleeve holder and a sleeve. In addition, the sleeve is given a double structure with the ceramic split sleeve and the metallic reinforcing sleeve.
However, there is dimensional tolerance (clearance) in each of components forming the optical module 1. Therefore, it is difficult to fix with high precision and maintain the center of the receptacle 4 where the ferrule 6 is received to the center position of the housing 3 which is an ideal fixing position.
Because of this, problems illustrated in FIG. 2 through FIG. 5 may occur. FIG. 2 through FIG. 5 are first through fourth views for explaining problems of the optical module 1 illustrated in FIG. 1. FIG. 3 is a cross-sectional view taken along a line C-C of FIG. 2. For the convenience of explanation, a position of the second stub part 4c of the receptacle 4 is illustrated in FIG. 3. An example where two receptacles 4 are provided in a single housing 3 is illustrated in FIG. 3.
The following are ideal. The brim parts 4b of the receptacles 4 are positioned, without gaps, in the groove part 8 formed in the convex part 7 provided inside the housing 3. The centers of the receptacles 4 where the ferrules 6 are received in the center position of the housing 3 with high precision. In addition, the centers of the receptacles 4, namely the centers of the ferrules 6 are consistent with the center of the ferrule 11 provided inside the optical connector 5.
However, since there is dimensional tolerance (clearance) in each of components forming the optical module 1, as illustrated in FIG. 2, a gap is formed inside the groove part 8 where the brim part 4b of the receptacle 4 is provided. The center position (indicated by one dotted line A in FIG. 2) of the ferrule 6 provided inside the receptacle 4 may not be consistent with the center position (indicated by one dotted line B in FIG. 2) of the ferrule 11 provided inside the optical connector 5.
As a result of this, a gap between a position of an optical axis of the ferrule 6 provided inside the receptacle 4 and a position of an optical axis of the ferrule 11 provided inside the optical connector 5 is generated so that coupling loss may be generated.
Details of this are discussed with reference to FIG. 3.
It is ideal that each of center positions in vertical and horizontal directions of the brim part 4b of the receptacle 4 provided in the groove part 8 and the second stub part 4c of the receptacle 4 inserted in a second stub part receiving hole 13 is consistent with center positions (indicated by one-dotted center lines in FIG. 3) in the vertical and horizontal directions of the housing 3. This ideal state is illustrated by solid lines in FIG. 3. A thick solid line indicates an ideal position of the brim part 4b. A thin solid line indicates an ideal position of the second stub part 4c. 
However, due to the dimensional tolerance (clearance), the brim part 4b may be formed in a position indicated by the thick dotted line in FIG. 3. The second stub part 4c may be formed in a position indicated by the thin dotted line in FIG. 3. In an example illustrated at the left side in FIG. 3, the brim part 4b and the second stub part 4c are provided in a position shifted in the vertical direction by distance y from the ideal position. In an example illustrated at the right side in FIG. 3, the brim part 4b and the second stub part 4c are provided in a position shifted to the right side in the horizontal direction by distance x from the ideal position.
As a result of this, a gap may be formed between a position of the optical axis of the ferrule 6 provided inside the receptacle 4 and a position of the optical axis of the ferrule 11 provided inside the optical connector 5, so that coupling loss of light may be generated.
Furthermore, in a case where large numbers of the optical modules 1 are mounted in parallel in the optical module mounting part for realizing the parallel transmission of a large number of optical signals, plural external line optical cables 2 to be connected to the optical modules 1 are collected together. Accordingly, a stress (bending moment) in the direction indicated by an arrow in FIG. 4 is applied to several of the external line optical cables 2 due to own weights of the external line optical cables 2.
Accordingly, since the receptacle 4 provided inside the housing 3 is mechanically fixed to the housing 3, due to the stress of the optical connector 5, a shift may be generated between the position of the optical axis of the ferrule 6 provided inside the receptacle 4 and the position of the optical axis of the ferrule 11 provided inside the optical connector 5, so that coupling loss of light may be generated and degradation of the optical output may be caused.
In addition, as illustrated in FIG. 5, in the optical module 1, the following are required for achieving a proper operation. That is, it is necessary to achieve reduction of radiation of electromagnetic waves indicated by black arrows in FIG. 5 from electronic components inside the optical module 1. In addition, a designated load bearing capacity against influence indicated by a white arrow in FIG. 5 of surges from outside of the optical module 1 is required.
Because of this, in the groove part 8 where the brim part 4b of the receptacle 4 is provided and the second stub part receiving hole 13 where the second stub part 4c of the receptacle 4 is inserted, it is necessary to provide the brim part 4b of the receptacle 4 and the second stub part 4c which are electric conductive bodies without forming gaps. The brim part 4b of the receptacle 4 and the second stub part 4c form a shield part indicated by a dotted line in FIG. 5 against the electromagnetic waves. By the shield part, as indicated by black arrows in FIG. 5, it is necessary to reduce the influence of EMI (Electro Magnetic Interference) based on electromagnetic waves from the electronic components inside the optical module 1.
Similarly, it is necessary to take measures for ESD (Electro-Static Discharge) by separating the shield part and SG (Signal Ground) from each other.
However, in a case where a gap is formed in the groove part 8 where the brim part 4b of the receptacle 4 is provided or is formed in the second stub part receiving hole 13 where the second stub part 4c of the receptacle 4 is inserted due to dimensional tolerance (clearance) of each of the components of the optical module 1 discussed with reference to FIG. 2 or a stress from outside of the optical module 1 discussed with reference to FIG. 4, it is difficult to reduce the influence of electromagnetic interference and take measures for electrostatic discharge.